Gold In Dentistry: Alloys, Uses And Performance

Gold In Dentistry: Alloys, Uses And Performance

Write briefly on the classification of casting gold alloys.
Or
Write a short note on the classification of casting gold alloys.
Answer:

Classification of Casting Gold Alloys:

In 1932, the National Bureau of Standards surveyed and later by ADA specification no. 5 and the American National Standard Institute (ANSI) has classified Gold Based Casting Alloys.

Depending on the Hardness:

• Type 1: Soft. VHN between 50–90 low strength.
• Type 2: Medium. VHN between 90–120 medium strength.
• Type 3: Hard. VHN between 120–150 high strength.
• Type 4: Extra hard. VHN between >150 extra high strength.

Type 1:  Soft or low-strength alloys are used for castings subjected to very slightly less stress-bearing areas.

For example, Inlays. The minimum yield strength is 80 MPa and VHN 50-90, minimum percent elongation is 18%.

Type 2: Medium-strength alloy is used for casting subjected to moderate stress.

• For example, Inlay, onlays, and full crowns.
• This has a minimum yield strength of 180 MPa and varies from 90-120 VHN, and the minimum percent elongation is 10%.

Type 3: Hard strength for castings subjected to high stress.

• For example,onlays, thin copings, pontics, crowns,s and saddles.
• The minimum yield strength is 270 MPa, minimum percent elongation is 5%.

Type 4: Extra hard strength for castings subjected to very high stress.

For example, Saddles, bars, clasps, thimbles, certain single units, and partial denture frameworks.

Type 1 and 2 are called as Inlay alloys while Type 3 and 4 are called crown and bridge alloys.

Depending on their Nobility:

• Noble
• Base metal.

Depending on the Functions

• Crown and bridge alloys
• Base metal alloys
• Removable partial denture alloys.

Based on the Color of the Alloy:

• Yellow gold alloy: Those with more than 60% gold and those with low gold or economy gold with 42 to 55% gold have a yellow color,
• For example, Noble high noble, predominantly base metals, and Japanese gold
• White gold alloy: Those with gold of more than 50% but palladium give a white color